SLUDGE DEWATERING - SNF Group

R I N G
The flocculated sludge flows over a filtration belt that is conveyed at a certain speed.
The water freed by the flocculation step is drained through the pores of the belt.
This elimination of water (the filtrate) leads to a thickening of the sludge at the end of the
conveyer belt. Picket fences resting on the belt are often used to enhance the gravity drainage.
Continuous pressure cleaning of the belt is necessary to prevent pore plugging.
The filtrate is returned to the beginning of the process while the thickened sludge is sent to
a temporary storage tank before dewatering.
3.2.1. Functionning principle:
3.2.2. Sludge conditioning before gravity belt:
KEY
PARAMETERS
LAB PROCEDURE/
SPREADSHEET
RECOMMENDATIONS
1
Sludge
+
Polymer
1 Flocculator
2 Guide
● Drainage speed
● Filtrate quality
● Floc formation speed
Laboratory evaluation
for belt press
and gravity belt
Filtrate
LAB TESTS PLANT TRIALS
Laboratory trials -
Gravity belt
& Belt filter
● Select the best charge density for
the sludge.
● Select the molecular weight best
suited for drainage.
2
3
3 Picket fences
4 Cleaning ramp
4
● Sludge flow
● Polymer flow
● Injection points
● Belt speed
● Belt cleaning
● Flocculator speed
● Thickened sludge concentration
● Filtrate quality
/
Thickened
sludge
Gravity belt
& Belt filter
performance sheet
● Polymer dosage should be between
3.0 and 10.0 kg/Dry Solids
Tonne (6 and 20 lbs/DT).
● The injection point of the polymer
is a key element and the drainage
speed will depend on it.
● Check carefully the water line.
d y n a m i c t h i c k e n i n g
13